Actuators are elements that cause a mechanical action when a control voltage or a control current is applied. The mechanical action is a movement of a movable element of the actuator. The result of this movement depends on the actuator concerned. In the following, mainly electrical switches are considered, that is to say that the movement of the movable element opens or closes an electrical contact. However, the invention may optionally be applied to other types of actuator, such as optical switches in which the movement of the movable element interrupts or modifies the optical path followed by a light beam.
MEMS electrical switches, actuated by an electromagnetic force produced by a small electrical coil integrated into a stationary part of the switch, the coil acting on a magnetic part borne by the movable element of the actuator, have already been proposed. Other actuators, the movable element of which is moved by an electrostatic force produced between two conducting planar electrodes located facing each other, one formed on a substrate of the actuator and the other borne by the movable element of the actuator, have also been proposed. U.S. Pat. No. 7,071,431 describes switches that operate on this principle. The movable element is an embedded cantilever beam parallel to the stationary substrate. The electrostatic force is applied between the substrate and the beam and acts to attract the free end of the latter toward the substrate. An electrical contact pad is borne on the end of the beam and comes into contact with one or more corresponding pads on the substrate when a sufficient control voltage is applied between the substrate and the beam.
Among others, important factors to take into consideration when designing an electrical switch are:                the actuating force required to switch the switch from a first state to another state: this force must be sufficient to move the movable element from a first position to a second position (and vice versa) despite any maintaining forces (for example magnetic forces) or restoring forces (for example the elasticity of the beam) that may act on the movable element when it is in the first position;        the voltage applied to obtain this force: it is desirable for this voltage to be as low as possible, notably so as to be compatible with the supply voltages conventionally used by integrated circuits (i.e. a few volts);        the current consumption, unavoidable if this switching from one state to another is to be obtained: a low consumption is desirable;        the current consumption necessary to maintain the switch in its state: ideally the state is maintained with no current consumption;        the force applied between the electrical contacts when the switch is closed: if the force is too small, the contact will be poor and the switch will only be able to pass a very small current (or else its lifetime is reduced); and        the distance between the electrical contacts when the switch is in an open state: it must be sufficient for there to be no risk of parasitic current conduction between the contacts in the open state of the switch, but not so large that the movement of the movable element of the switch is too great.        
All these parameters are interdependent. For example, there is a relationship between the actuating force and the applied control voltage and a relationship between the distance between the contacts in the open state and the actuating force necessary to close the switch.